1. Field of the Invention
This invention relates to the field of electronic analog computers.
2. Description of the Prior Art
Electronic analog circuits are most typically constructed using high-gain differential operational amplifiers. The theory is easily understood and integrated circuit operational amplifiers are readily available from a number of manufacturers. Unfortunately, operational amplifiers are extremely slow under operating conditions. The operating characteristics of operational amplifiers are typically rated by the product of gain and bandwidth, which, for the widely used 741 amplifier is given as about one million. Since a gain of from 100 to 1000 is needed to make operational amplifiers operate in computer circuits according to theory, the bandwidth is from 1 to 10 kHz. Some more modern operational amplifiers are capable of significantly better but still low bandwidths.
I have previously published a description of a system for building active filters without operational amplifiers in "Build Active Filters without Op Amps," EDN, published on Feb. 20, 1986, pages 246 and 248. In this article I discussed the use of fixed-gain amplifiers for use in active filters, but I did not arrive at that time at the use of fixed-gain amplifiers in analog computers.